AN APPRAISAL OF CERTAIN FACTORS WHICH INFLUENCE TOUGHNESS RESTORATION(DE-EMBRITTLEMENT) IN SOME TEMPER EMBRITTLED LOW-ALLOY STEELS

This paper describes and assesses the various factors which affect the degree of de-embrittlement, DELTAFATT, of a selection of embrittled l ow alloy steels after a simple tempering heat treatment. It has been s hown that the degree of de-embrittlement was variable and could be div ided into two separate sets of data depending upon the embrittled frac ture mode characteristics. The steels which failed in a wholly intergr anular manner, predominantly the nickel-containing steels, exhibited l arge DELTAFATT values of between 150 and 250-degrees-C. However, the n on-nickel-containing steels, viz. the Cr-Mo and Cr-Mo-V steels, fractu red in a mixed mode fashion, which comprised intergranular failure and transgranular cleavage, and exhibited much lower levels of toughness rejuvenation. When the raw data were corrected for grain size effects it was clear that the bulk phosphorus content of the steels significan tly influenced the extent of de-embrittlement. Also when the de-embrit tlement data were portrayed in terms of the embrittled condition tough ness, FATT(EMB), and corrected to a constant composition and grain siz e, it was observed that the degree of toughness restoration, DELTAFATT , was insensitive to FATT(EMB).